The Nobel Peace Prize web site was hacked and an exploit of a zero-day Firefox vulnerability was used to install malware on visitor's PC's. While the Nobel site is no longer an active threat, the vulnerability remains, and other sites may be compromised. Disabling Javascript or using the NoScript extension will protect users until a patch is released.
http://blog.mozilla.com/security/2010/10/26/critical-vulnerability-in-firefox-3-5-and-firefox-3-6/